SSL tests failing for channel_binding with OpenSSL <= 1.0.1

Hi all,
(Jeff Davis in CC)

As $subject tells, any version of OpenSSL not including
X509_get_signature_nid() (version <= 1.0.1) causes the SSL tests to
fail.  This has been introduced by d6e612f.

We need to do something similar to c3d41cc for the test, as per the
attached.  I have tested that with OpenSSL 1.0.1 and 1.0.2 to stress
both scenarios.

Any objections to this fix?

Thanks,
--
Michael